Obesity and smoking have both repeatedly been shown to be serious health hazards. However, they can also be overcome. If Spector's study is right, the finding may be one more reason to go for a smoke-free life at a healthy weight, even if it takes hard work and time to get there.

Cellular Aging Study

The women in Spector's study were all twins aged 18-76 years. The group consisted of 45 pairs of identical twins and 516 pairs of nonidentical twins.

The researchers examined the length of the telomeres in their white blood cells. Telomeres are the tips of the chromosomes, which contain DNA. They gradually shorten over a lifetime. That's a normal part of the aging process. Telomere length was checked by isolating white blood cells from the women's blood samples.

Estimated Effects

Smoking and obesity were linked to shorter telomere length, say the researchers.

Assuming their results pan out, the researchers were able to estimate the number of years lost to cigarettes -- or extra pounds.

The difference in telomere length between being lean and being obese corresponds to 8.8 years of aging.

Smoking (previous or current) corresponds on average to 4.6 years of aging.

Smoking a pack per day for 40 years corresponds to 7.4 years of aging.

Keep in mind that those time spans refer to telomere length, not overall aging.

"Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries -- cigarettes and obesity," write the researchers.

They point out that there was "considerable variation" in telomere length between participants and call for larger studies on the topic.